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Date:   Mon, 21 Feb 2022 15:17:47 +0100
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Subject: Re: [PATCH v4 09/15] crypto: dh - implement private key generation
 primitive for ffdheXYZ(dh)
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To:     Nicolai Stange <nstange@suse.de>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        "David S. Miller" <davem@davemloft.net>
Cc:     =?UTF-8?Q?Stephan_M=c3=bcller?= <smueller@chronox.de>,
        Torsten Duwe <duwe@suse.de>,
        David Howells <dhowells@redhat.com>,
        Jarkko Sakkinen <jarkko@kernel.org>,
        linux-crypto@vger.kernel.org, linux-kernel@vger.kernel.org,
        keyrings@vger.kernel.org
References: <20220221121101.1615-1-nstange@suse.de>
 <20220221121101.1615-10-nstange@suse.de>
From:   Hannes Reinecke <hare@suse.de>
In-Reply-To: <20220221121101.1615-10-nstange@suse.de>
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On 2/21/22 13:10, Nicolai Stange wrote:
> The support for NVME in-band authentication currently in the works ([1])
> needs to generate ephemeral DH keys for use with the RFC 7919 safe-prime
> FFDHE groups.
> 
> In analogy to ECDH and its ecc_gen_privkey(), implement a
> dh_safe_prime_gen_privkey() and invoke it from the ffdheXYZ(dh) templates'
> common ->set_secret(), i.e. dh_safe_prime_set_secret(), in case the input
> ->key_size is zero.
> 
> As the RFC 7919 FFDHE groups are classified as approved safe-prime groups
> by SP800-56Arev3, it's worthwhile to make the new
> dh_safe_prime_gen_privkey() to follow the approach specified in
> SP800-56Arev3, sec. 5.6.1.1.3 ("Key-Pair Generation Using Extra Random
> Bits") in order to achieve conformance.
> 
> SP800-56Arev3 specifies a lower as well as an upper bound on the generated
> key's length:
> - it must be >= two times the maximum supported security strength of
>    the group in question and
> - it must be <= the length of the domain parameter Q.
> 
> For any safe-prime group Q = (P - 1)/2 by definition and the individual
> maximum supported security strengths as specified by SP800-56Arev3 have
> been made available as part of the FFDHE dh_safe_prime definitions
> introduced with a previous patch. Make dh_safe_prime_gen_privkey() pick
> twice the maximum supported strength rounded up to the next power of two
> for the output key size. This choice respects both, the lower and upper
> bounds given by SP800-90Arev3 for any of the approved safe-prime groups and
> is also in line with the NVME base spec 2.0, which requires the key size to
> be >= 256bits.
> 
> [1] https://lore.kernel.org/r/20211202152358.60116-1-hare@suse.de
> 
> Signed-off-by: Nicolai Stange <nstange@suse.de>
> ---
>   crypto/Kconfig |   1 +
>   crypto/dh.c    | 140 +++++++++++++++++++++++++++++++++++++++++++++++--
>   2 files changed, 138 insertions(+), 3 deletions(-)
> 
Reviewed-by: Hannes Reinecke <hare@suse.de>

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		           Kernel Storage Architect
hare@suse.de			                  +49 911 74053 688
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